When I began my research as professor of complementary medicine in Exeter 17 years ago, I was entirely open to homeopathy. I had been treated for many years by a homeopathic doctor, my father had practised homeopathy and I had begun my medical career in a homeopathic hospital. But now my job was to apply science to the field and, to do this properly, one needs to be not just open but also critical.

The first thing any critical mind has to note is that the two basic assumptions of homeopathy fly in the face of science. Like does not cure like and diluting remedies ad infinitum does not render them stronger but weaker. But perhaps there was something entirely new and undiscovered here, the stuff of Nobel prizes that revolutionises our understanding of nature?

The acid test, I thought, was whether homeopathic remedies behave differently from placebos when submitted to clinical trials. So we conducted several trials and published many summaries of the studies done worldwide. The results were sobering. Today there are about 200 clinical trials and the totality of this evidence fails to show that homeopathic remedies work.

But what about patients' experience? What about my own experience as a patient and later as a clinician? In fact, tonnes of data shows that people get better after seeing a homeopath. This is why homeopaths are adamant that their treatments work. Can this wealth of experience be overruled by scientific evidence?

When one begins to analyse this contradiction rationally it very quickly dissolves into thin air. The empathic encounter with a homeopath, the expectation of the patient, the natural history of the disease and many other factors all provide ample explanation for the fact that patients can improve even when they receive placebos.

This leads to the vexatious question: what is wrong with giving placebos to patients as long as they help? The answer, I'm afraid, is a lot. This strategy would mean not telling the truth to patients and thus depriving them of fully informed consent. This paternalistic approach of years gone by is now considered unethical.

Also, placebo effects are unreliable and usually short-lived. Moreover, endorsing homeopathic placebos in this way would mean that people may use it for serious, treatable conditions. Furthermore, if we allow the homeopathic industry to sell placebos we should do the same for big pharmaceutical companies – and where would this take us? Crucially and somewhat paradoxically, we don't need a placebo to generate a placebo effect. If I give my headache patient an aspirin and do this, as all good doctors should, with empathy, time and understanding, the patient will benefit from a placebo effect plus the pharmacological effect of the aspirin. If I prescribe her a homeopathic remedy, I quite simply deprive her of the latter. It is difficult to argue that this approach would be in the interest of my patient.

What follows is straightforward: homeopathy is yet another beautiful theory destroyed by ugly facts.